In the last fifty years, the plastics industry has seen enormous growth such that plastic materials and products are now essential to society. Plastic production in countries like Japan has reached around 15 million tonnes per year, and this results in about 9 million tonnes per year of related waste, 50% of which is associated with municipal solid waste.
There are increasing problems with plastics disposal, and internationally plastics recycling accounts for a small proportion of material recovery, with the rest being disposed either through land-filling or burning in incinerators. Plastic materials do not degrade readily and can leach toxic elements in landfill, whilst conventional burning often generates hazardous emissions such as dioxins.
Worldwide the steel industry is facing pressure to minimise its impact on the environment by improving the efficiency of energy and resource utilisation. For example, particular efforts have been made to reduce the carbon intensity of a blast furnace. One strategy of energy management of a blast furnace involves the reduction of fuel or coke consumption. As a substitute fuel, plastic injection into the tuyeres of a blast furnace has been proposed to reduce CO2 emissions, because plastics have a combustion energy that is at least as high as the pulverised coal normally injected, and they have a higher ratio of hydrogen to carbon, resulting in less CO2 produced as a combustion product.
Plastic addition to other types of steelmaking furnaces is known, including to electric arc furnaces (EAF). For example, U.S. Pat. No. 5,554,207 discloses a process in which EAF waste dust is combined with waste plastic to form a solid, which is then added to the EAF. Similarly, JP2004-052002 discloses a process in which waste plastics are knedaded together with steel dust to form a soft solid which is added to the EAF. Neither document is concerned with the addition of an additive to promote slay foaming.